1. Technical Field of the Invention
The present invention relates generally to an obstacle recognition system for use in traveling control of automotive vehicles, and more particularly, to an obstacle recognition-system capable of distinguishing vehicles present ahead of a system equipped vehicle from other objects at improved reliability and confidence levels.
2. Background of Related Art
Automotive obstacle recognition systems are known in the art which are designed to emit radar waves such as light waves and milimetric waves and receive a signal reflected from a detectable zone to recognize an object present ahead of the vehicle. As such systems, there have been proposed a collision alarm apparatus which measures the distance to an obstacle such as a preceding vehicle and issues an alarm and a cruise control apparatus which controls the speed of the vehicle to keep the distance to a preceding vehicle. These apparatuses are required to identify desired preceding vehicles as objects for the issuance of alarm and the cruise control with high accuracy. In other words, it is important to eliminate errors that obstacles on the side of a road are recognized as preceding vehicles. To this end, the prior art system distinguishes obstacles on the side of a road from preceding vehicles based on the fact that the obstacles are usually stationary and do not exist on the same lane as a controlled vehicle. Specifically, if a detected object is determined as a stationary object based on a change in position of the obstacle in a width-wise direction of the controlled vehicle and also determined as existing out of the same lane as the controlled vehicle based on the position in the width-wise direction of the controlled vehicle, the possibility that the detected object is an obstacle on either of the sides of a road is determined to be high.
It is, however, difficult to distinguish obstacles on the side of a road from preceding vehicles accurately under a variety of circumstances. For example, when a vehicle enters a curve, it is possible that a road sign provided on the side of a road will be recognized as a stationary vehicle present ahead in error. Further, when a vehicle is traveling before a downhill road or near the end of an uphill road, billboards or road signs located above a road surface which will not be detected when the vehicle is traveling on a level road may be detected as obstacles present ahead of the vehicle. Conversely, when the vehicle is traveling before an uphill road or near the end of a downhill road, the road itself or white lines and cat's-eyes on the road surface may be viewed forward of the vehicle. Therefore, the road itself and the while lines may be recognized as preceding vehicles traveling at a constant interval away from the vehicle, while the cat's-eyes may be recognized as stationary vehicles, which is an inherent performance limitation of the prior art systems designed to detect obstacles in two-dimensional direction: width-wise direction and longitudinal direction of the vehicle using a one-dimensional scan over a given angle in the width-wise direction of the vehicle.